Happy to breed in the city? Urban food resources limit reproductive output in Western Jackdaws

Abstract

Urban areas expand worldwide, transforming landscapes and creating new challenging habitats. Some bird species, mainly omnivorous feeding on human waste and cavity nesters, commonly breed in these habitats and are, therefore, regarded as urban‐adapted. Although urban areas may provide new nesting sites and abundant human waste, the low breeding success found in some of these species suggests that the poor protein content in human waste might limit breeding parameters. We investigated whether the breeding success of a cavity nester and omnivorous species commonly breeding in urban areas, the Western Jackdaw (Corvus monedula), depended on the availability of good‐quality non‐urban food. We approached the objective by combining a literature review and experiments in the field. With the literature review, we compared jackdaw populations in different habitats across Europe and found that clutch size and number of fledglings per pair decreased with distance to non‐urban foraging grounds, even after controlling for the effect of colony size, latitude, and climate. In two experiments, we tested whether the breeding success of urban pairs could be increased by supplementing high‐quality food, first only during egg formation and second also until chick fledging. Food supplementation during egg formation led to larger eggs and higher hatching success than in urban control nests, but this did not result in higher chick survival. However, when food supplementation was prolonged until fledging in the second experiment, we observed a significant increase of nestling survival. These findings highlight that research and management actions should not only focus on species displaced by urbanization, but also on “urban‐adapted” species, as they might be suffering from a mismatch between availability of nesting sites in buildings and adequate non‐urban food resources. In these cases, nest sites should be provided in or close to adequate food resources.

Growing in Cities: An Urban Penalty for Wild Birds? A Study of Phenotypic Differences between Urban and Rural Great Tit Chicks (Parus major)

“…Because nestlings rely on protein-rich diet during their development, this arthropod impoverishment is probably a major nutritional constraint for urban developing great tits (McIntyre et al, 2001;Shochat et al, 2004). Supporting this idea, food supplementation experiments have been shown to result in increased body size and nestling survival in urban birds (Zanette et al, 2003;Schoech et al, 2007;Heiss et al, 2009;Meyrier et al, 2017) and crossfostering experiments demonstrated that reduced nestling body size in urban areas is indeed related to the rearing urban environment (e.g., Seress et al, 2012).…”

Dynamic species distribution models reveal spatiotemporal habitat shifts in native range‐expanding versus non‐native invasive birds in an urban area

“…within 50 m) consistently ranked among the most important predictors of jackdaw breeding distribution. In non-urban habitats, jackdaws typically prefer to breed in wide, open natural tree cavities (Johnsson et al 1993, Balen et al 2002, but a recent review by Meyrier et al (2017) concluded that these birds may be attracted to cities because buildings provide ample cavities, Figure 2. Yearly relative importance of the predictors as a percentage for ensemble models used to predict the distributions of (a) Psittacula krameri and (b) Corvus monedula.…”

Animal Cognition in an Urbanised World

“…While urban environments may favour enhanced learning and problem-solving abilities in theory, the costs associated with urban life may also impair cognitive performance (Griffin et al, 2017b). For example, diet has an important influence on cognitive development (e.g., Pravosudov et al, 2005;Kitaysky et al, 2006) and studies of urban birds suggest that nutritional constraints may partly explain the general trend for lower reproductive success in urban habitats (Sumasgutner et al, 2014;Biard et al, 2017;Meyrier et al, 2017;Seress et al, 2020). Taken together, these findings imply that poor-quality food in urban habitats could impair the cognitive development of growing chicks (e.g., Arnold et al, 2007), but this possibility has yet to be tested explicitly.…”